The Impact Factor is calculated by dividing the number of citations in the JCR year by the total number of articles published in the previous two years.

Dear Madhukar Baburao Deshmukh

Is it necessary to be cited in different journals?

The calculation is based on a two-year period and involves dividing the number of times articles were cited by the number of articles that are citable.

Calculation of 2010 IF of a journal:

A = the number of times articles published in 2008 and 2009 were cited by indexed journals during 2010.B = the total number of "citable items" published in 2008 and 2009.

A/B = 2010 impact factor 

There is a bit of "confusion" happening here. First, my impression is that there are different ways of calculating impact factors, some methods based on a single year and other methods spanning more than a single year - in which case the number of years spanned is usually indicated (and usually on a journal's website).

Second, the original questioner has added another question - one that, although it's not directed to me, I'll attempt to answer by saying that I think it isn't "necessary to be cited in different journals". However, all things being equal, it's good to be cited in high quality journals. If researchers' submissions are accepted by the same high-quality journal, I see no problem in those submissions being cited when they are published by that journal.

The Impact Factor is calculated by dividing the number of citations in the JCR year by the total number of articles published in the two previous years. An Impact Factor of 1.0 means that, on average, the articles published one or two year ago have been cited one time.........